Air-cooled turbine blade

ABSTRACT

An air-cooled turbine blade ( 1 ) is provided in the cavity ( 5 ) of the blade body ( 3 ) with an insert ( 6 ) made of a shape memory alloy. Due to the contraction of the insert ( 6 ) after a certain temperature threshold value is exceeded, the cooling system ( 12 ) of the turbine blade ( 1 ) is enlarged in the interior. The size of the cooling system ( 12 ) (effectiveness of the cooling, cooling-air quantity, size of cooling passages) is therefore advantageously dependent upon the ambient temperature.

[0001] The invention deals with an air-cooled turbine blade according to the preamble of claim 1. Such turbine blades are used as guide or moving blades, for example, in gas turbines.

[0002] It has been known practice for a long time to cool those parts of thermal turbomachines which are subjected to hot gas, that is, for example, turbine blades of gas turbines, by means of a cooling medium in order to be able to increase the temperature of the hot gas, on the one hand, and to prolong the service life of the parts concerned, on the other hand, due to lower material loading. For this purpose, cooling holes are provided in the wall of the turbine blade and other cooling systems are provided in the interior of the turbine blade. On the one hand, the inside of the turbine blade is cooled in this way with the cooling air by dissipation of the heat to the outside. On the other hand, the outside of the blade is cooled by a film which forms on the surface of the turbine blade.

[0003] In the case of the turbine blades in the prior art, it is also known to provide the cavity with one or more inserts in order to obtain a certain cooling structure. Such inserts are widespread and are described, for example, in publications DE-A-23 20 581, EP 0 534 207, EP 0 182 588 or also in DE-A-1476 790. In these disclosures, there are in some cases, in addition to the insert, further built-in components in the interior in order to cool certain parts of the turbine blade in an improved manner relative to other parts or to utilize the cooling air more effectively. Thus there are ribs on the wall of the cavity, which together with the insert form clearly defined cooling passages, constrictions for improved cooling, for example of the pressure side of the blade, or cooling holes in the insert for the (impingement) cooling of the leading edge or of one of the two sides.

[0004] A turbine blade has also been disclosed by U.S. Pat. No. 4,859,141, which provides an insert which is made of a shape memory alloy. When a certain temperature threshold value is exceeded, the insert expands and in this way bears free of play against the internal geometry.

[0005] For the development of turbine blades, which are continuously leading to an increase in the hot-gas temperature of gas turbines, it is essential to provide improved cooling systems. By means of the inserts disclosed by the prior art, however, it is not possible to vary the size of the cooling system, in particular the size of the cooling passages, as a function of the temperature of the hot gas, since the insert is rigid and the size of the cooling system/cooling passages does not change as a function of the temperature during the operation of the gas turbine. This therefore has an especially adverse effect, since it is necessary, by means of an improved cooling-air feed, to cool certain regions of the turbine blade more intensively relative to other regions of the turbine blade as a function of the temperature acting from outside.

[0006] The aim of this invention is to avoid the abovementioned disadvantages. The invention achieves the object of designing an air-cooled turbine blade with an insert which regulates the cooling (effectiveness of the cooling, cooling-air quantity, size of cooling passages) in the interior of the cavity as a function of the temperature of the hot gas during operation of the gas turbine.

[0007] According to the invention, this is achieved in a turbine blade according to the preamble of claim 1 by virtue of the fact that the size of the insert, after a temperature predetermined by the composition of the shape memory alloy is exceeded, is changed in such a way that the cooling system is changed, i.e. enlarged or reduced in size, as a result.

[0008] In order to reduce the overall size of the insert, it is especially advantageous if a strap which accommodates two overlapping ends of the insert is provided in the insert. In the thermally activated state, the insert can be reduced in size overall by the two ends being pushed one over the other.

[0009] By only individual portions being provided with a shape memory alloy, the insert can advantageously be used to specifically cool certain parts of the turbine blade in an intensified manner. To this end, it may be necessary to provide one or more “articulations” in the form of bends or curves in the shape memory alloy, which permit the local change in size of the insert. This may be effected, for example, in the vicinity of the leading edge of the turbine blade, on the pressure or suction side, or over the height of the blade body.

[0010] It may also be advantageous to use the insert in connection with ribs arranged radially or axially on the inner wall of the cavity. In this case, the insert covers the ribs and reduces the size of the cooling passages resulting from the ribs owing to the fact that the insert projects into the intermediate space between the ribs. When the insert contracts, the ribs are covered in a flush manner and the cooling passages are thus enlarged.

[0011] In order to utilize the effect of the contraction in the thermally activated state in an improved manner and also to ensure retention of the insert on the blade body of the turbine blade, it is necessary to mechanically fasten the insert by brazing or welding to one or more points at the wall of the blade body, to the ribs, to the tip, or to the platform of the turbine blade.

[0012] There may advantageously be cooling holes in the insert in order to intensify the effect of the cooling.

[0013] For the insert, shape memory alloys, such as, for example, NiTi, Cu—Zn—Al or also Cu—Al—Ni, have been disclosed by the prior art. The alloys may in principle be used for the insert in the exemplary embodiments disclosed.

[0014] In the drawing:

[0015]FIG. 1 shows a turbine blade (guide or moving blade) of a gas turbine with an insert according to the invention,

[0016]FIG. 2a shows a section through the turbine blade along line II-II in FIG. 1 with a first embodiment of an insert according to the invention, which is not activated thermally,

[0017]FIG. 2b shows a section through the turbine blade along line II-II in FIG. 1 with the first embodiment of an insert according to the invention, which is activated thermally,

[0018]FIG. 2c shows a section through the turbine blade along line II-II in FIG. 1, with a second embodiment of an insert according to the invention, which is not activated thermally,

[0019]FIG. 2d shows a section through the turbine blade along line II-II in FIG. 1, with the second embodiment of an insert according to the invention, which is activated thermally,

[0020]FIG. 2e shows a section through the turbine blade along line II-II in FIG. 1, with a second embodiment of an insert according to the invention, which is not activated thermally,

[0021]FIG. 2f shows a section through the turbine blade along line II-II in FIG. 1, with the second embodiment of an insert according to the invention, which is activated thermally,

[0022]FIG. 3a shows a section through the turbine blade along line III-III in FIG. 2a, with a further embodiment of an insert according to the invention, which is not activated thermally,

[0023]FIG. 3b shows a section through the turbine blade along line III-III in FIG. 2a, with the embodiment according to FIG. 3a of an insert according to the invention, which is activated thermally in a certain region,

[0024]FIG. 3c shows a section through the turbine blade along line III-III in FIG. 2a, with a further embodiment of an insert according to the invention, which is not activated thermally, and

[0025]FIG. 3d shows a section through the turbine blade along line III-III in FIG. 2a, with the embodiment according to FIG. 3a of an insert according to the invention, which is activated thermally.

[0026] Only the elements essential for the invention are shown. The same elements are designated the same in different figures.

[0027]FIG. 1 shows a turbine blade 1 of a gas turbine. This turbine blade is normally a guide or moving blade which is fastened to the rotor or the stator of the gas turbine. For the purpose of fastening the turbine blade 1, a fastening means 7 on a platform 2 is provided in the top region of the turbine blade 1. A blade body 3 is fastened to the platform 2. The platform 2 has a surface 4 exposed to the hot gases of the gas turbine. The blade body 3 is provided with a cavity 5, in which an insert 6 is located. For the purpose of cooling, the cavity 5 is provided with a cooling system 12 (not shown in any more detail in FIG. 1) The cooling system 12 enables the walls of the blade body 3 to be cooled by cooling air which has been introduced into the cavity 5. So that the cooling air can leave the blade body 3 again, cooling holes 8 are provided on the surface of the blade body 3. The number of cooling holes shown in FIG. 1 and their arrangement on the surface are merely exemplary and depend on the type of insert of the turbine blade 1. Numerous cooling systems have been disclosed by the prior art and are therefore not explained in any more detail here.

[0028]FIG. 2a shows a section through the blade body 3 along line II-II in FIG. 1. The blade body 3 has a suction side 9, a pressure side 10 and a leading edge 11. The insert 6 is located in the cavity 5. The aim of the cooling system 12 is to introduce cooling air in a specific manner between the insert 6 and the cavity 5. For example, the cooling air can be introduced in the center of the insert 6 and can penetrate between the insert 6 and the wall of the blade body 3 through cooling holes 8 which in FIG. 1 are present in an exemplary manner in the front part of the insert 6. The cooling air can leave the turbine blade 1 again through the cooling holes 8 which are present in the wall of the blade body 3.

[0029] The insert 6 is made of a so-called shape memory alloy, SMA. The properties of shape memory alloys are summarized, for example, in The Metals Handbook, Desk Edition, Second Edition, Ed. by J. R. Davis, ASM International, pages 668/669. Shape memory alloys, which consist of nickel and titanium with a proportion (% by weight) of 49-51% Ni and 51-49% Ti, are known in principle. Such an alloy is available on the market, for example under the name Nitinol. In addition, there are further shape memory alloys in the tertiary system Cu—Zn—Al or Cu—Al—Ni. These types of shape memory alloys are suitable in principle for the insert 6 in the present patent application.

[0030] Shape memory alloys have the property of returning to their original shape (memory effect) if a temperature established by the material is exceeded. This memory effect is utilized in the subject matter of the present application. In FIG. 2a, which shows the insert 6 in expanded form, at a temperature below the temperature threshold value of the shape memory alloy, the insert 6 is provided with a strap 16. The strap 16 consists of two overlapping ends of the insert 6. During operation of the gas turbine, the predetermined temperature is exceeded by admission of the hot gases to the turbine blade 1 and the insert 6 contracts due to the two ends being pushed one over the other. As a result, the insert 6 is reduced in size overall. This state is shown in FIG. 2b. The cooling system 12 is advantageously enlarged due to the reduction in size of the insert 6. The quantity of the cooling air and the size of the cooling system 12 increase and thus serve to cool the walls of the blade body 3 in an intensified manner. It is also conceivable to reduce the size of the cooling system at other locations in order thus to improve the cooling of those parts of the turbine blade 1 which are subjected to greater thermal loading relative to the parts which are subjected to less thermal loading.

[0031]FIG. 2b schematically shows with the aid of arrows the possible cooling mechanisms of a turbine blade 1 inside the cooling system 12. Impingement cooling 18 is obtained in the vicinity of the leading edge 11 by impingement of cooling air on the leading wall. The cooling air sweeping along the walls provides for convection cooling 20. In addition, by discharge from the cooling holes 8 located in the wall of the turbine blade 1, further film cooling 19 occurs at the outer surface of the blade body.

[0032]FIGS. 2c and 2 d show a second embodiment of an insert 6 according to the invention. FIG. 2c shows the insert, which is not activated thermally, below the predetermined temperature of the shape memory alloy, and FIG. 2d represents the insert 6 in the thermally activated state due to temperature increase. The special feature of this embodiment is that the properties of the shape memory alloy specifically act only on the tip of the insert 6. This means that only the tip, which is located in the front region in the vicinity of the leading edge 11 of the turbine blade 1, is made of the shape memory alloy, and a type of articulation 17 is located between this tip and the rear part. This articulation 17 provides for the “bending-in” of the insert at a predetermined location. It may be present in the form of bends, preliminary folds or curves in the shape memory alloy. By means of this embodiment, the leading edge 11, which is especially stressed, is supplied with cooling air and is especially cooled there.

[0033]FIGS. 2e and 2 f are analogous to FIGS. 2c and 2 d. They show the shape memory alloy in a thermally activated/thermally inactivated embodiment. Unlike FIGS. 2c and 2 d, the tip of the shape memory alloy is provided with a plurality of “articulations” 17, so that thermal activation leads to folding of the tip.

[0034]FIGS. 3a and 3 b show a further embodiment of the insert according to the invention along section III-III in FIG. 2a. The blade body 3 is shown in a section over the height. Since it is sufficient to show a detail in order to illustrate the invention, only a small portion of the wall of the blade body 3 is illustrated. This portion schematically shows the blade body 3 from the platform 2 with the surface 4 up to the blade tip 14. The wall may be the suction side 9 or also the pressure side 10 of the turbine blade 1. The insert 6 is located in the hollow body 5. Due to the corrugated shape of the insert 6, cooling passages 15 form between the wall of the blade body 3 and the insert 6. These cooling passages 15 are reduced in size in FIG. 3a by the thermal inactivation. FIG. 3b shows the thermally activated shape. In a top region, the insert 6 is made of a shape memory alloy. This results in enlarged cooling passages 15 a there and thus improved cooling there. The unchanged cooling passages 15 b are located in the bottom region of the blade body 3 close to the blade tip 14 of the turbine blade 1. Due to this embodiment, specific cooling in a region of the turbine blade 1 defined beforehand is possible. An embodiment in which the cooling capacity is improved overall would also be conceivable.

[0035]FIGS. 3c and 3 d show a further embodiment of the insert according to the invention along section III-III in FIG. 2a. The blade body 3 is again shown in a section over the height. Ribs 13 are located on the inner wall of the hollow body in the axial direction. The wall may be the suction side 9 or also the pressure side 10 of the turbine blade 1. In principle, it makes no difference whether the following explanation refers to radial or axial ribs 13. Cooling passages 15 are produced between the ribs 13. The ribs 13 and the cooling passages 15 are covered by the insert 6 in such a way that separate cooling passages 15, separated from one another, are produced. In FIG. 3a, protruding material of the insert 6 projects into the cooling passages 15. In this case, the insert 6 is not activated thermally due to a low temperature. The equivalent to FIG. 3c, with an insert 6 activated thermally by a temperature increase, is shown in FIG. 3d. The insert 6 is reduced in size by contraction and in this way lies so as to be spread in a flush manner across the ribs 13. The cooling passages 15 are enlarged in this state.

[0036] In order to utilize the effect of the contraction in the thermally activated state in an improved manner and also to ensure retention of the insert 6 on the blade body 3 of the turbine blade 1, it is necessary to mechanically fasten the insert 6 by brazing or welding to one or more points at the wall of the blade body 3, to the ribs in the interior of the cavity 5, to the blade tip 14, or to the platform 2 of the turbine blade 1. A bayonet fastener or a bayonet catch is equally conceivable, so that the insert latches in place on insertion at a certain location and is rigidly fastened at this location.

[0037] The invention is not restricted to the exemplary embodiments described but relates in particular to any combination of features disclosed in the description.

[0038] List of Designations  1 Turbine blade  2 Platform  3 Blade body of the turbine blade 1  4 Surface of platform 4  5 Cavity  6 Insert  7 Fastening means of the turbine blade 1  8 Cooling holes  9 Suction side of blade body 3 10 Pressure side of blade body 3 11 Leading edge of blade body 3 12 Cooling structure 13 Ribs 14 Blade tip of blade body 3 15 Cooling passages 15a Cooling passages, widened 15b Cooling passages, narrowed 16 Strap 17 Articulation in insert 6 18 Impingement cooling 19 Film cooling 20 Convection cooling 

1. A turbine blade (1) of a gas turbine, consisting of a platform (2), a blade body (3) connected to the platform (2), having at least one cavity (5) in the interior of the guide or moving blade (3), in which cavity (5) a metallic insert (6) is inserted, and which cavity (5) has a cooling system (12), the metallic insert (6) being made of a shape memory alloy, and the blade body (3) having a leading edge (11), a suction side (9) and a pressure side (10), and a blade tip (14), characterized in that the size of the insert (6), after a temperature predetermined by the composition of the shape memory alloy is exceeded, is changed in such a way that the cooling system (12) is changed, i.e. enlarged or reduced in size, as a result.
 2. The turbine blade (1) as claimed in claim 1 , characterized in that the insert (6) has a strap (16) in which two ends of the insert (6) are pushed one over the other at increased temperature and in this way the insert (6) is reduced in size overall.
 3. The turbine blade (1) as claimed in claim 1 , characterized in that merely one part of the insert (6) is made of a shape memory alloy and thus only one part of the cooling system (12) in the cavity (5) is enlarged by a change in the size of the insert (6) when the predetermined temperature is exceeded.
 4. The turbine blade (1) as claimed in claim 3 , characterized in that the part of the insert (6) which is made of a shape memory alloy is distributed over the height of the blade body (3).
 5. The turbine blade (1) as claimed in claim 3 , characterized in that only the tip of the insert (6) is made of a shape memory alloy, the tip being located in the region of the leading edge (11) of the blade body (3), and thus the cooling system (12) in the cavity (5) is enlarged in the region of the leading edge (11) when the predetermined temperature is exceeded.
 6. The turbine blade (1) as claimed in claim 1 , characterized in that there are ribs (13) on the wall in the interior of the cavity (5) in the radial or axial direction, so that the cooling system (12) is designed as cooling passages (15) between the ribs (13), and these ribs (13) are covered by the insert (6) over the height of the guide or moving blade (3), in which case protruding material projects into the cooling passages, and the cooling passages (15) are covered in a flush manner by the insert (6) and are thus enlarged when the insert (6) is reduced in size by the temperature increase.
 7. The turbine blade (1) as claimed in one of claims 3 to 6 , characterized in that there is an articulation (17) between the parts of the insert (6) which are made of a shape memory alloy and the parts of the insert (6) which are not made of a shape memory alloy.
 8. The turbine blade (1) as claimed in one of the preceding claims, characterized in that the insert (6) is mechanically fastened by brazing or welding to discrete points at the cavity (5), to the platform (4), to the blade tip (14) or to the ribs (13) of the cooling system (12).
 9. The turbine blade (1) as claimed in one of the preceding claims, characterized in that the insert has cooling holes (8).
 10. The turbine blade (1) as claimed in one of the preceding claims, characterized in that the insert (6) is made of a shape memory alloy consisting of NiTi or CuZnAl or CuAlNi.
 11. The turbine blade (1) as claimed in claim 10 , characterized in that the insert (6) is made of a shape memory alloy having a composition of 49-51% by weight Ni and 51-49% by weight Ti. 